JPS6351983B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a fluorescent standard glass for a fluorescent glass dosimeter used to calibrate measured values in a fluorescent glass dosimeter that measures exposure radiation doses. [Technical background of the invention and its problems] Fluorescent glass dosimeters generally use phosphate glass containing silver ions (hereinafter referred to as silver-activated phosphate glass) as a detector; emits fluorescence when excited by ultraviolet light with a wavelength of 300 to 400 nm, and the fluorescence intensity is proportional to the exposure radiation dose, so the radiation dose can be determined by measuring the fluorescence intensity. To measure the radiation dose, for example, a mercury lamp is used as a light source for excitation of ultraviolet rays, and after passing the light from the mercury lamp through an optical filter to block light of a predetermined wavelength or more, the transmitted ultraviolet rays are transferred to a rectangular parallelepiped-shaped silver activator. The light is applied perpendicularly to one side of the phosphate glass.
Then, the fluorescence emitted from the silver-activated phosphate glass by ultraviolet excitation is taken out in a direction perpendicular to the incident light beam, and the transmitted light is filtered to block light outside a predetermined wavelength range.The output signal is converted by a photomultiplier tube and the fluorescence intensity is determined. I try to measure it. However, in this measurement method, even with the best silver-activated phosphate glass, the fluorescence intensity before exposure is about 150 mR when converted to a gamma ray dose value, and the measurement accuracy is insufficient for measuring an exposure dose of about 10 mR. The problem is that it cannot be obtained. In order to solve the above problems, for example,
As described in Japanese Patent Publication No. 47-51919 and Japanese Patent Publication No. 50-38352, fluorescent glass dosimeters employing a pulse measurement method have been proposed. When the fluorescent centers of silver-activated phosphate glass are stimulated with a very short pulse of ultraviolet light, the fluorescent centers emit fluorescence.
In this fluorescence decay characteristic, if the time when the fluorescence intensity reaches the maximum value of 1/e is defined as the decay time, then the fluorescence decay time of silver activated phosphate glass after exposure to radiation is
It is 3.2μsec. In contrast, the fluorescence decay time before radiation exposure is extremely short at 0.3 μsec. Therefore, in the pulse measurement method, as shown in Figure 3, the decay time of fluorescence based on the glass matrix before radiation exposure is approximately 1/10 of the decay time of fluorescence based on the fluorescence center due to radiation exposure, so the observation is difficult. By delaying the time, these can be completely separated, making it possible to measure doses as low as 10 mR with high precision. However, fluorescent glass dosimeters based on the pulse measurement method have the following drawbacks. Mn ²⁺ ions, Sm ³⁺ ions, which are used in conventional continuous light measurements, are used as fluorescence standard glasses to calibrate dose values during measurements.
When fluorescent glasses containing Nd ³⁺ ions are used, the fluorescence decay time of these glasses is shorter than that of silver-activated phosphate glass exposed to radiation. The delayed observation time used to observe fluorescence due to radiation exposure of activated phosphate glass does not allow for sensitive fluorescence intensity measurements and accurate calibration of dose values. When using silver-activated phosphate glass that has been irradiated with radiation with a known dose as the fluorescence standard glass, the disadvantage of the difference in fluorescence decay time mentioned above is solved, but silver-activated phosphate glass By natural radiation exposure of ~100mR,
Because the fluorescence intensity changes over time, 10mR
In low-dose measurements, it causes measurement errors and does not serve as a fluorescence standard glass. [Purpose of the Invention] The present invention has been made in view of the above circumstances, and is suitable for use in measuring low doses of about 10 mR as a glass for calibrating dose values measured by fluorescent glass dosimeters based on the pulse measurement method. The purpose of the present invention is to provide a fluorescent standard glass for fluorescent glass dosimeters that improves the performance of fluorescent glass dosimeters. [Summary of the Invention] In order to achieve the above object, the present invention was discovered as a result of various experimental studies by the present inventors. The fluorescence decay time and fluorescence spectrum are similar to those of silver-activated phosphate glass after exposure to radiation, and the fluorescence intensity is γ
This is a fluorescent standard glass that has characteristics such that the radiation dose value is 5R or less. i.e. SiO ₂ 50-80%, B ₂ O ₃ 0-25%, Al ₂ O ₃ 0-
As a fluorescent agent in base glasses containing 10%, alkali metal oxides 5-25%, and divalent metal oxides 5-25%.
Added Eu ₂ O ₃ 0.002~0.05%, wavelength 300 ~
The time at which the fluorescence intensity reaches its maximum value of 1/e is the decay characteristic of fluorescence emitted by 400nm ultraviolet excitation.
This is a fluorescent standard glass for fluorescent glass dosimeters in the range of 1.5 to 6 μsec. The basic glass composition of the present invention is a conventional soda-lime glass or borosilicate glass, and the composition itself is not new. Also, glass battu
_It is also already known to create fluorescent glasses by adding _Eu2O3 . However, in order to apply these fluorescent glasses to the above-mentioned pulse measurement type fluorescent glass dosimeter, a certain amount of fluorescence is generated by the excitation ultraviolet pulse, and the decay time and fluorescence spectrum of the fluorescence are determined by the silver after exposure to radiation. The present inventors were the first to elucidate that a glass with characteristics similar to those of activated phosphate glass and whose fluorescence intensity is 5R or less when converted to a γ-ray dose value can be used as a fluorescence standard glass. That's what I got. [Examples of the Invention] Examples of the invention will be described with reference to tables. of different amounts to the basic glass composition shown in the table.
Approximately _1300-1400 batches each with added _Eu2O3
The molten glass was melted at a temperature of 40°C for 4 hours, and the molten glass was cast into a predetermined shape, and a sample with a predetermined shape was produced through the steps of cutting, roughening, and polishing. For these samples, we used a fluorescent glass dosimeter (Toshiba FGD-8) that applied nitrogen gas laser pulses to excitation ultraviolet light.
was used to measure the fluorescence intensity converted into a γ-ray dose value.

【table】

〔Effect of the invention〕

As described above, the present invention has SiO ₂ 50 in weight percentage.
~80%, _{B2O3 0-25} %, _{Al2O3 0-10} %, alkali metal oxides 5-25%, divalent metal oxides 5-25% with _Eu2 as a fluorescent agent in the base glass. _O3 from 0.002
It is a fluorescent standard glass made by adding 0.05% by weight,
The fluorescence decay time and fluorescence spectrum produced by the excitation ultraviolet pulse are almost similar to those of silver-activated phosphate glass after exposure to radiation, and a constant amount of fluorescence is emitted by the excitation ultraviolet pulse regardless of the presence or absence of radiation exposure. , and its fluorescence intensity is less than 5R when converted into a gamma ray dose value, making it ideal as a fluorescent standard glass for calibrating low-dose measurements of fluorescent glass dosimeters based on the pulse measurement method. This fluorescent standard glass can be used in combination with the fluorescent glass dosimeter to improve measurement accuracy.
Significant improvement of ±3% at low dose of 10mR.
It also has excellent effects such as sufficient stability for long-term use. Note that even if a thin film of MgF ₂ or the like is deposited on the surface of the glass of the present invention for the purpose of improving its weather resistance, no effect is observed on the above-mentioned performance.

[Brief explanation of drawings]

Figure 1 is a curve diagram showing the relationship between the amount of Eu ₂ O ₃ added and the fluorescence intensity of the glass of the present invention, and Figure 2 is a curve diagram showing the relationship between the fluorescence intensity and fluorescence decay time of the glass of the present invention and its base glass. Figure 3 is a curve diagram showing the relationship between fluorescence intensity and fluorescence decay time of silver-activated phosphate glass; Figure 4 is a curve diagram showing the relationship between fluorescence wavelength and fluorescence intensity emitted by the glass of the present invention. , FIG. 5 is a curve diagram showing the relationship between the wavelength of fluorescence and fluorescence intensity emitted by silver-activated phosphate glass exposed to radiation.

Claims (1)

[Claims] 1 SiO ₂ 50-80%, B ₂ O ₃ 0-25% by weight percentage,
Al ₂ O ₃ 0-10%, alkali metal oxide 5-25%,
It is made by adding 0.002 to 0.05% of Eu ₂ O ₃ as a fluorescent agent to a base glass containing 5 to 25% of divalent metal oxide, and the fluorescence intensity is the highest in the decay characteristics of fluorescence emitted by excitation of ultraviolet light with a wavelength of 300 to 400 nm. 1. A fluorescent standard glass for a fluorescent glass dosimeter, characterized in that the time for 1/e of is in the range of 1.5 to 6 μsec.